1. Field of the Invention
The invention is directed to a new process, and products made thereby, employing a novel catalyst for the production of polyphenylene ethers (polyphenylene oxides). The improved polyphenylene ethers made by this process have reduced odor.
2. Brief Description of the Prior Art
The polyphenylene ethers and processes for their preparation are known in the art and described in numerous publications, including Hay, U.S. Pat. Nos. 3,306,874 and 3,306,875. Other procedures are described in Van Dort, U.S. Pat. No. 3,365,422, Bennett and Cooper, U.S. Pat. Nos. 3,639,656, 3,642,699, 3,733,299, 3,838,102, 3,661,848 and 4,092,294, and Olander, U.S. Pat. No. 4,055,553. All of these patents are incorporated herein by reference.
The processes most generally used to produce the polyphenylene ethers involve the self-condensation of a monovalent phenol in the presence of an oxygen-containing gas and a catalyst.
Improved catalyst systems have been developed for the preparation of polyphenylene ethers by the oxidative coupling of 2,6-di-substituted phenolic compounds. Such systems are disclosed in the above-noted U.S. Pat. No. 4,092,294. This patent discloses a catalyst which comprises a copper compound; a diamine wherein the two amino nitrogens are separated by at least two and no more than three carbon atoms, and the carbon atom to which the amino nitrogen are attached is aliphatic; a tertiary amine and a bromine-containing compound selected from the group consisting of hydrogen bromide, alkali metal bromides, alkaline earth metal bromides, 4-bromophenols and mixtures thereof plus an amount of a primary or secondary monoamine, most frequently a secondary monoamine of the formula RNHR' wherein R and R' are lower alkyl.
According to the prior art, this primary or secondary amine has a major effect on the reaction rate, as shown in U.S. Pat. Nos. 4,092,294 and 4,477,651. Almost all of the primary or secondary amine becomes incorporated into the polyphenylene ether. Polymers made in this way typically have between 600 and 1000 ppm of nitrogen bound in the polymer. The incorporation of the amine is believed to be mainly as so-called Mannich end groups having the structure: ##STR1## This incorporation has both advantages and disadvantages.
In regard to advantages, the amine groups in the polyphenylene ether can be lost thermally during processing or blending, resulting in the generation of reactive functional groups on the polymer, such as quinone methide structures that can couple with each other or with other materials (e.g. rubber, high impact polystyrene, etc.) to increase the molecular weight and to generate grafted products with such other materials. This beneficial effect aids compatibilization and may improve impact strength of blends. When this self-coupling is carried out by heating the polymer at the end of the polymerization, the process is known as "IV jump," in other words, the intrinsic viscosity reflecting the molecular weight "jumps" upward, on the order of a factor of 2. This is a desirable phenomenon, since the mechanical properties of the polymer generally improve with molecular weight.
On the other hand, in regard to disadvantages, the slow release of the secondary amine from the polymer even at ambient temperatures, presumably by a chemical elimination reaction, causes the polymer to emit an unpleasant odor.
The other amines used in the typical copper-based catalyst system for making polyphenylene ethers, i.e. typically a branched alkyl-substituted diamine, a tertiary amine and a quaternary ammonium compound, do not become a significant part of the polymer and do not contribute to odor appreciably, in contrast to the primary or secondary monoamine component.
Means have hitherto been sought for overcoming this amine-related odor problem. One approach taught by U.S. Pat. No. 4,806,602 is to end-cap the polymer by means of a further reaction with the polymer. However, running such reactions with a polymer is a costly and troublesome step, and it is difficult to achieve completeness of reaction.
Therefore, it is one object of my invention to overcome the odor problem by replacing the secondary amine if this could be accomplished without any significant loss in reaction rate or polymer properties. One polymer property that is important to retain is the molecular weight, as evidenced by the intrinsic viscosity. Another related property that would be desirable to maintain is the "IV jump" property, as described herein above. Therefore, further objects of my invention are to overcome the odor problem without losing molecular weight and preferably without losing the "IV jump" property.
The aforedescribed objectives are achieved in my improved process for making polyphenylene ethers by replacing the secondary dialkylamine component of the catalyst system by certain unsaturated compounds which are not amines, and which thus cannot generate amine structures in the polymer which are associated with undesirable odor. This total or substantially total replacement of the secondary monoamine by the unsaturated compound surprisingly leaves the catalyst system unchanged in effectiveness, and with the preferred unsaturated compounds, it also leaves the "IV jump" property of the polymer intact.